Present methods of non-contact current measurements in conductors often consists of the use of iron or other ferrous types of magnetic materials configured so as to couple the magnetic field surrounding a current carrying conductor in a transformer configuration. These present methods are often accurate and are widely employed in measuring a.c. currents in wires and other electrical conductors. The generic term for the instruments now widely employed is "current clamp", or "clamp-on current probe". These provide a means of rapidly measuring the a.c. current by surrounding the conductor with a magnetic circuit which is configured as a transformer which is designed for a convenient ratio for measurement to provide, for example, one milliampere per ampere, or one millivolt per ampere. The output of these clamp-on current probes is then read out on a meter or attached via wires to a multimeter. Manufacturers and distributors of such clamp-on current probes are, for example, Fluke Corporation, Amprobe Instruments, AEMC Instruments, Fieldpiece Corporation, Hewlett-Packard Corporation, and many others. A second common non-contact method of measuring current utilizes the Hall effect. A Hall element placed in the region of a magnetic field provides an output voltage proportional to the field. Hall element devices are often utilized for both a.c. and d.c. non-contact current measurements in wires and other conductors and are also widely available from these same manufacturers and distributors of a.c. clamp-on current probes.
The use of a ferromagnetic material in a non-contact current probe provides the advantage that good accuracy is often obtained. The major disadvantages are that these clamps require complete access to the wire or conductor so that the current clamp must completely surround the wire or conductor, that the characteristics of the ferromagnetic material are non-linear, the process of taking a reading is slow, and the current clamps are large, awkward and sometimes impossible to use when wires are in confined spaces.
In practice, for many cases, the electrical worker cannot easily surround a conductor with a conventional current clamp because the conductor or wire may be fastened to, or very close to a wall or ceiling and it would be awkward and very inconvenient to use a current clamp. Also, in some cases, the non-linearity can be a serious problem when large as well as very small currents are to be measured because the hysteresis curve of ferromagnetic types of materials is, in general, non-linear, and will cause reading errors.
Non-contact voltage sensing instruments are now often employed by many electrical workers. These instruments provide a rapid indication of the existence of a voltage on an insulated wire by simply bringing the tip of the instrument close to or touching an insulated or bare wire carrying voltage. Thousands of such instruments are utilized in the electrical industry to determine whether or not there is a voltage on the wire or conductor. Usually these instruments light a light emitting diode, (LED), and/or sound a buzzer. Some of these instruments can distinguish between 120 volts, 240 volts, and 480 volts. Some of these instruments can determine the voltage accurately.
Basically, these instruments are in common use because they are inexpensive, pocket-sized, and provide a very quick decision of when a wire, conductor, or terminal is "hot", (has voltage), and is not.
Many of these voltage sensors are very simple in design. Typically, they utilize a digital IC gate which is triggered by a pulse input. The IC then lights an LED to indicate the presence of an a.c. voltage. Because of their simplicity, low cost, and pocket size, these devices are widely employed in electrical industries. Other types of voltage sensors are also employed which are more accurate and more complex.
The present invention provides means to overcome the disadvantages of the conventional current clamp and provides a quick indication of the current flow or of the power by simply touching the insulated or bare conductor or wire with the probe as described below. By combining the current probe described here with a voltage sensor, the electrical worker will be provided with a much more versatile pocket sized instrument, and can measure power also. In many cases, the voltage is constant, and the apparent power is easily determined by scaling the output voltage to read out the power output directly.